1. Field of the Invention
The present invention relates to a magnetic head and a method of manufacturing the same, and more particularly, it relates to a magnetic head which is employed for a magnetic recorder/reproducer such as a video tape recorder (VTR), a digital audio tape recorder (DAT) or the like.
2. Description of the Prior Art
In recent years, a recording signal has been highly densified in a magnetic recorder/reproducer such as VTR or DAT, and a metal tape having high magnetic resistance, which employs ferromagnetic metal powder of Fe, Co, Ni or the like as magnetic powder, has been used in correspondence to such a high-density signal.
For example, a metal tape having high magnetic resistance of Hc=1400 to 1500 Oe is employed for a small video tape recorder called 8 mm VTR. This is because a recording medium which can reduce the wavelength for recording a signal is required in order to miniaturize a magnetic recorder/reproducer.
When a conventional magnetic head formed of only ferrite is employed for recording a signal in such a metal tape, on the other hand, a magnetic saturation phenomenon takes place since saturation magnetic flux density of ferrite is about 5500 Gs at the most, and hence performance of the metal tape cannot be sufficiently effectuated. In order to cope with the metal tape having high magnetic resistance, therefore, the magnetic head must have high saturation magnetic flux density in the vicinity of a gap of a magnetic core in addition to high frequency characteristics and abrasion resistance, which are generally required for the core of the magnetic head. In order to satisfy such requirement, there has been proposed a magnetic head for a metal tape, which is called a composite type magnetic head. In this magnetic head, a portion close to a magnetic gap, which easily causes a magnetic saturation phenomenon, is prepared from a magnetic metal material such as permalloy, Sendust or amorphous magnetic substance, for example, having larger saturation magnetization than that of ferrite employed for a magnetic core. The composite type magnetic head is excellent in reliability, magnetic property, abrasion resistance and the like.
FIG. 1 is a perspective view showing the appearance of a conventional magnetic head. Referring to FIG. 1, ferromagnetic metal thin films 3a and 3b formed of a material having high saturation magnetic flux density such as Sendust are provided in the vicinity of a magnetic gap 2, which is formed by abutting a pair of magnetic core halves 1a and 1b prepared from ferromagnetic oxide such as Mn--Zn ferrite through a nonmagnetic material. The magnetic core halves 1a and 1b are joined with each other by a glass member 4, to define a coil groove 5.
In the aforementioned composite type magnetic head, the ferromagnetic metal thin films 3a and 3b are adhered to/formed on upper surfaces of ferromagnetic oxide substrates, which are subjected to specular processing, by sputtering. However, portions close to junction interfaces between the ferromagnetic metal thin films and the substrates of ferromagnetic oxide are nonmagnetized by mutual diffusion and chemical reaction between the elements, inconsistency in crystal structure or the like, to serve as false gaps which exert a bad influence on the performance of the magnetic head.
As shown in FIG. 1, such false gaps are defined in junction interfaces 6a and 6b between the magnetic core halves 1a and 1b and the ferromagnetic metal thin films 3a and 3b, in addition to the original working magnetic gap 2.
In order to suppress the occurrence of such false gaps, junction interfaces 6a and 6b between magnetic core halves 1a and 1b and ferromagnetic metal thin films 3a and 3b are made nonparallel to the surface defining an original working magnetic gap 2, as shown in FIG. 2. Thus, there has also been proposed a composite type magnetic head, which is so formed that no bad influence is exerted on the performance of the magnetic head even if false gaps are defined. The magnetic head having such a structure is complicated in manufacturing process and at a high cost, as compared with that shown in FIG. 1. The conventional magnetic heads shown in FIGS. 1 and 2 are disclosed in Japanese Patent Laying-Open Gazettes Nos. 175122/1983 and 229210/1985, for example.
A method of manufacturing the conventional magnetic head shown in FIG. 1 is now described. FIGS. 3A, 3B, 4A, 4B and 5 are perspective views sequentially showing steps in an exemplary method of manufacturing the conventional magnetic head.
Referring to FIGS. 3A and 3B, specular polishing is first performed on a pair of substrates 7a and 7b, which are formed of ferromagnetic oxide such as Mn--Zn ferrite. Thereafter ferromagnetic metal thin films 3a and 3b of 1 to 10 .mu.m in thickness, which are formed of Sendust or the like, and nonmagnetic thin films 8a and 8b of SiO.sub.2 or the like, which are adapted to define gaps, are sequentially formed by sputtering.
Then, as shown in FIGS. 4A and 4B, track width regulating grooves 9a are formed in the upper surface of the first substrate 7a while track width regulating grooves 9b, coil grooves 5 and glass rod receiving grooves 10 are formed in the upper surface of the second substrate 7b by a dicing saw or the like, respectively. In order to form the track width regulating grooves 9a and 9b, the coil grooves 5 and the glass rod receiving grooves 10, the nonmagnetic thin films 8a and 8b, the ferromagnetic metal thin films 3a and 3b and the substrates 7a and 7b are scraped off by a rotating grindstone or the like.
Referring to FIG. 5, the pair of substrates 7a and 7b are washed and thereafter portions 11a and 11b corresponding to track width are abutted with each other in high accuracy. Glass rods 12 are inserted in the glass rod receiving grooves 10. Then the abutted pair of substrates 7a and 7b are heated to 600.degree. to 700.degree. C., thereby to melt the glass rods 12. Thus, the track width regulating grooves 9a and 9b are filled with glass members 4. A block is thus formed through glass junction of the pair of substrates 7a and 7b. Thereafter the block is cut along broken lines I--I and II--II shown in FIG. 5 and ground/polished, thereby to complete the magnetic head shown in FIG. 1.
In the aforementioned manufacturing method, however, the ferromagnetic metal thin films 3a and 3b are formed by sputtering or the like, and hence internal strain is caused between the substrates 7a and 7b and the ferromagnetic metal thin films 3a and 3b by difference in thermal expansion coefficient therebetween. Thus, as shown in FIGS. 4A and 4B, the ferromagnetic metal thin films 3a and 3b are subjected to strain caused by mechanical working upon cutting work of the track width regulating grooves 9a and 9b etc. with the dicing saw, and are separated from each other.
Japanese Patent Laying-Open Gazette No. 287017/1986, for example, discloses a method of manufacturing a magnetic head for solving the aforementioned problem. FIGS. 6A, 6B, 7A, 7B, 8A and 8B are perspective views sequentially showing steps in the method of manufacturing the magnetic head, which is disclosed in the said literature.
As shown in FIGS. 6A and 6B, a pair of substrates 7a and 7b, which are formed with ferromagnetic metal thin films 3a and 3b and nonmagnetic thin films 8a and 8b in sequence, are prepared similarly to FIGS. 3A and 3B.
Then, as shown in FIGS. 7A and 7B, portions to be provided with track width regulating grooves are selectively removed from the nonmagnetic thin film 8a and the ferromagnetic thin film 3a formed on the first substrate 7a by ion beam etching or the like. Thus exposed is the upper surface of the substrate 7a, which is provided with first strain parting grooves 12a. Further, portions to be provided with track width regulating grooves, coil grooves and glass rod receiving grooves are selectively removed from the nonmagnetic thin film 8b and the ferromagnetic metal thin film 3b formed on the second substrate 7b by ion beam etching or the like. Thus exposed is the upper surface of the substrate 7b, which is provided with first strain parting grooves 12b, 12c and 12d.
As shown in FIGS. 8A and 8B, recessing is thus performed on the portions of the substrates 7a and 7b exposed in the aforementioned etching step by a dicing saw or the like, thereby to define track width regulating grooves 13a and 13b, coil grooves 13c and glass rod receiving grooves 13d.
Thereafter portions 11a and 11b corresponding to track width are abutted with each other in high accuracy similarly to the step shown in FIG. 5, thereby to form a block through glass junction of the substrates 7a and 7b. The block is cut and ground/polished, to complete the magnetic head.
According to the aforementioned manufacturing method, recessing is mechanically performed by the dicing saw or the like on regions from which the nonmagnetic thin films 8a and 8b and the ferromagnetic metal thin films 3a and 3b are previously removed by ion beam etching or the like. Thus, strain applied to the ferromagnetic metal thin films 3a and 3b by mechanical working is reduced, whereby the rate of separation of the ferromagnetic thin films 3a and 3b is reduced.
FIGS. 9, 10A and 10B are partial sectional views showing a step in which a substrate is pressed against a rotating grindstone in the process of mechanical recessing shown in FIGS. 1A and 1B. Referring to FIG. 9, a rotating grindstone 14 is introduced into regions 12a from which portions of a nonmagnetic thin film 8a and a ferromagnetic metal thin film 3a are previously removed, thereby to form track width regulating grooves 13a. In order to precisely form the track width regulating grooves 13a, the rotating grindstone 14 is introduced into a substrate 7a to be in contact with side surfaces of the remaining portions of the ferromagnetic metal thin film 3a.
After first grooves are formed by a rotating grindstone 14a, second grooves are formed by another rotating grindstone 14b, as shown in FIGS. 10A and 10B. The rotating grindstones 14a and 14b are brought into contact with side surfaces of remaining portions of a ferromagnetic metal thin film 3a, or pass through portions extremely close to the remaining portions of the ferromagnetic metal thin film 3a. Thus, a ferromagnetic metal thin film is separated by mechanical impact or vibration caused by a rotating grindstone, even if the former is not directly cut by the latter. Namely, it is considered that separation of a ferromagnetic metal thin film is caused by mechanical impact or vibration which is applied thereto even if no mechanical strain is applied to the ferromagnetic metal thin film by a rotating grindstone, since the ferromagnetic thin film has various strain components resulting from condition changes caused before and after formation of the film.
Further, such strain components existing in the ferromagnetic thin film may be integrated into elastic strain, to cause separation of the ferromagnetic metal thin film in employment of the magnetic head.